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Mechanical and Biochemical Effect of Monopolar Radiofrequency Energy on Human Articular Cartilage

An In Vitro Study

Ko Yasura, MD^*, Yasuaki Nakagawa, MD^*,, Masahiko Kobayashi, MD^*, Hiroshi Kuroki, PT and Takashi Nakamura, MD^*

From the ^* Department of Orthopaedic Surgery, Graduate School of Medicine, and the Department of Physical Therapy, School of Health Sciences, Faculty of Medicine, Kyoto University, Kyoto, Japan

Address correspondence to Yasuaki Nakagawa, MD, Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, 54 Kawahara-Cho, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan (e-mail: ynaka{at}kuhp.kyoto-u.ac.jp).

Background: There are growing concerns about thermal chondroplasty using radiofrequency energy to treat partial-thickness cartilage defects. However, most studies emphasize effects on chondrocyte viability, and other factors such as mechanical properties are less studied.

Hypothesis: Radiofrequency energy may cause significant effects on articular cartilage other than chondrocyte viability.

Study Design: Controlled laboratory study.

Methods: Human osteoarthritic cartilage samples were obtained from total knee arthroplasty, and monopolar radiofrequency energy was applied using commercially available equipment. Material properties (compressive stiffness, surface roughness, and thickness) just before and after thermal treatment were determined using ultrasound. A series of biochemical analyses were also performed after explant culture of the samples.

Results: The cartilage surface became smoother by radiofrequency energy, whereas cartilage stiffness or thickness was not altered significantly. Collagen fibrils, especially in the superficial layers, were converted to denatured form, whereas proteoglycan contents released in the media as well as retained in the tissue remained unchanged. The concentrations of matrix metalloproteinases (MMP-1 and MMP-2) were reduced remarkably.

Conclusion: Radiofrequency energy is able to create a smooth cartilage surface and reduce catabolic enzymes at the cost of collagen denaturation and chondrocyte death in the superficial layers. The stiffness of the cartilage is not changed at time zero.

Clinical Relevance: Further animal as well as clinical studies will be necessary to fully evaluate the long-term effects of radiofrequency energy.

Key Words: radiofrequency energy (RFE) • thermal chondroplasty • articular cartilage • ultrasound • collagen • matrix metalloproteinase (MMP)